ReservoirPy v0.3.1

• Adding teacher nodes: nodes can be used as teachers for other nodes when training online.
• Adding warmup parameter in for offline learning (and removing transient parameter from Ridge).
• Adding new matrices initializers in mat_gen (more flexible than the old ones).
• Adding node dtype parameter to change parameter type.
• Adding bias and bias_scaling in Reservoir.
• Fixing tutorials (#51 #61)

Full Changelog: v0.3.0...v0.3.1